I've overwintered heucheras, palace purple for a number of years. Also dianthus, columbines lamium, lamiastrum. There aren't exactly tall plants but I'm usually using foliage annuals for height in pots. Guess this is another experiment!

Your zone is a bit warmer than mine, so you may have better luck than I've had with perennials in pots surviving. For me, the only way I've had success is to bury the whole pot in the garden for the winter. Doing this I've had probably 95% success for survival. I've tried some hostas and creeping jenny in whiskey barrels that were too big to move no less bury, and they never came back. On the other hand, I have heard you can be lucky if you stick with perennials that are rated for 2 or 3 zones colder than you are. So if I were you I'd try some zone 2 plants and see how they work. It's worth a shot. It would be interesting to hear what other plants people have wintered in pots.
As for using clay pots, I'd be careful with them. Like you said, the expanding and contracting may not be a good thing for them, but maybe someone else may have more experience with them than I have.
Good luck,
Laurie

I don't have much of a problem having things overwinter in pots. Our winters pretty much stay cold enough that once things freeze, they stay frozen. Do yours? If not, I think pots would have a tendency to have more varying temperatures than the ground, and thus things might go through too many freeze/thaw cycles to survive. That is PURELY conjecture, however. Clay pots certainly have a tendency to break with freezing and thawing. I find plain clay pots break far faster than glazed ones. You probably wouldn't lose them all in one winter...it's difficult to predict. I've had some break the first winter, and some last for 10 years.

My preferred method for overwintering in pots is the one Laurie described.....burying the pots.

I have over-wintered a non-hardy perennial in my potato cellar where it stays a couple of degrees above the freeze point. Putting the pots in an unheated area, that stays just above freezing, should preserve your clay pots.

A third option. After the first frosts ...remove the perennials from the pots and plant them directly in the ground. Dig them and repot in the spring.

Jan

The only perennials I have ever overwintered in a pot with no extra care are my hardy opuntia cacti (they are in a cedar trough). Once a foxglove survived. It was a weird thing to do, but I turned the pot upside down on it and mulched over top, turned it back up in the spring, and it lived. Didn't flower though. I am NOT advising this, I'm just mentioning it out of interest.

Nothing else has ever come back in pots but I haven't tried it much as I don't expect success. I know offhand I have lost scabious this way.

I have seen the nursery over winter some of their plants in 1 gallon pots......they dig them into the ground and throw saw dust over them. Not all their plants come back in spring though.

Clay pots won't make it through our winters here....they just crumble....but I don't know for your zone.

Sierra

Oh yeah further to clay pots - you can buy ones that are specifically "frost-proof". I sometimes forget my pots outside over the winter (like, all the time - ahem...) so I know they don't break. And the ones that aren't frost proof DO break, every time.

I'm really partial to cedar planters for a number of reasons, one being that you can leave them outside. They also seem to dry out slower but that could be just me.

I have never over wintered perennials in pots, but I do about 30, so I thought adding perennials would cut on cost. I am either going to put them in 1- pots and bury them in the ground or 2- I have a back room which stays 40deg. Which might be easier than putting them all in the ground, because the room is 40 deg. And dark and that's what they require, right? Or I have a unheated garage, it does get 25 below here sometimes in the winter, but the garage would be no wind and somewhat warmer. They would be in plastic container's. Anyone have any ideas?